Disadvantages of validating ideas on PH?

B2B: Yes.
B2C: No, hmm may be.

ProductHunt is used by Entrepreneurs, Wannabe Entrepreneurs and to some extant Early Stage Investors. So if you're building a product for them, then their validation could be useful provided all other variables associated with the platform ends up in your favour during the launch.

But, if yours is a consumer product, unless it's shiny, has something to do with cats, you are unlikely to find those whose problem your product solves at PH.

Have an audience before launching there. I've seen the most successful people launch there with an actual audience they've built beforehand.

If you launch too early you product idea might be copied

Product Hunt isn't an audience. https://stackingthebricks.com/dont-launch-product-hunt/

This is a really great question. I view Product Hunt not as a validation engine but as an amplification engine. There was a time with Product Hunt where you could really validate a product. That’s more reserved for the Product Hunt Makers discussions now. Posting something to PH now is all about amplification.

I launched on Product Hunt and had 3 upvotes in 1 month - terrible. We're a consumer product for youth sports teams (https://wildkard.io), so PH was probably the wrong place for us to launch and expect attention.

If I look at fellow indiehackers that have launched on Producthunt successfully.
Most have done it not initially but once they have had a decent amount of users or twitter followers.

Agree with the one comment where due to low votes your product will lost.

I used to think of PH or HN as a magic bullets, build launch there and you are set.

However defining and acquiring your target user is much more important. You target user might not be viewing or familiar with PH. Go where your users are / hang out.